An oil depot (sometimes referred to as a tank farm) is an industrial facility for the storage of oil and petrochemical products. Oil depots often include terminals where the oil or petrochemical product is dispensed into road tankers or other methods of transportation such as barges or pipelines. Products dispensed from an oil terminal are generally in their final form and are suitable for delivery to customers. The petrochemical products dispensed at a terminal are often referred to as wholesale fuel.
Terminal technology has remained largely unchanged for many years, The road tanker, or tanker truck, enters the terminal to obtain wholesale fuel. The tanker truck is connected to the terminal to begin the process of fueling. The vast majority of terminals use a bottom fill system wherein the fuel fill line attaches to the bottom of the tanker and fills the tanker from the bottom. When the tanker truck is filling, fuel vapors are produced which must be safely disposed of. These fuel vapors may be either combusted or recovered with both methods having advantages and disadvantages. When a tanker truck is filling, a vapor vent line is connected to a the tanker which transports the fuel vapors from the tanker truck to either a recovery unit or a combuster.
Many terminals have begun using is vapor recovery unit (hereinafter VRU) to recover the fuel vapors which are produced when filling a tanker truck, or other fuel transportation vehicle. A typical VRU unit has at least two adsorber vessels filled with adsorbent, such as activated carbon, a vacuum pump or other source of vacuum, a return pump and a plurality of valves. The adsorbers are properly piped and valved so that one adsorber is currently receiving vapors while the other adsorber is in a regeneration mode. When the loading process begins at the terminal, vapors are transported to the active adsorber where they are adsorbed. Once an adsorber vessel is nearly saturated or, more commonly, cycles for a predetermined cycle time, the vessel is switched to a regeneration mode and the vapors are directed to the second adsorber vessel while the first adsorber regenerates.
Regeneration occurs when the adsorbed fuel vapor is removed from the activated carbon so that the carbon in the adsorber vessel is cleansed and capable of adsorbing more fuel vapors. The fuel vapor is commonly removed by vacuum and purge air stripping. A vacuum pump extracts the fuel vapor from the saturated adsorbent and transfers it to an absorption column. The absorption column vessel contains a packing material to increase the efficiency of the absorption process. The fuel vapors from the adsorber flow up through the absorption column while liquid fuel flows down through the packing. The liquid fuel absorbs the vapors retained in the packing. The now liquefied fuel is pumped to the storage tank for reuse. All fuel vapors not absorbed in the absorption column are returned by use of a recycle line to the adsorber to be recovered.
The VRU is typically run in fifteen-minute cycles wherein one adsorber is online and accepting fuel vapors while the other adsorber is offline and in regeneration mode. Some terminals operate at full capacity putting a larger load on the VRU. Such operations tend to strain the efficiencies of the VRU's as the adsorbers commonly cannot regenerate as quickly as they become saturated. Therefore, the terminal load rack capacity exceeds the VRU capacity and the VRU may go into total shutdown where both adsorbers regenerate at the same time and the load rack operations are shutdown.
Therefore it is an object of this invention to maximize the terminal loading capacity by controlling the load rack fuel dispensing with the VRU performance outputs to prevent undesirable shutdown of the fuel dispensing at terminal facilities.